System.NullReferenceException Error Csharp

Question

Getting the error :

System.NullReferenceException

for the below code on a C# Windows form.

try
{
    foreach (DataGridViewRow row in dataGridView2.Rows)
    {
        if (row.Cells["txtAttendance_Status"].Value.ToString() == "Attended")
        {
            row.Cells["txtStatus"].Value = true;
        }
        else if (row.Cells["txtAttendance_Status"].Value.ToString() == "Not Attended")
        {
            row.Cells["txtStatus"].Value = false;
        }
        else
        {
            row.Cells["txtStatus"].Value = false;
        }
    }
}

catch (Exception ex)
{
    MessageBox.Show("Error", ex.ToString());
}

Below is the table :

Include your full code as its not clear you are `inserting` or `getting` from database. — Md Farid Uddin Kiron, Mar 05 '20 at 11:00
[ToString() vs Convert.ToSring()](https://stackoverflow.com/questions/2828154/difference-between-convert-tostring-and-tostring) — Vijay, Mar 05 '20 at 11:00
Also include your full error to understand more on the issue. — Sathish Guru V, Mar 05 '20 at 11:02

Arys · Answer 1 · 2020-03-05T12:03:45.710

1

Before running this line

row.Cells["txtAttendance_Status"].Value.ToString()

you have to check the content of row.Cells["txtAttendance_Status"].Value is not null.

You are performing a ToString() over a Null

EDIT: The code

switch (row.Cells["txtAttendance_Status"].Value)
{
    //only if its string with value Attended
    case string s when s.Equals("Attended", StringComparison.InvariantCultureIgnoreCase):
        row.Cells["txtStatus"].Value = true;
        break;
    default:
        //All other cases "Not Attended", null or whatever
        row.Cells["txtStatus"].Value = false;
}

edited Mar 05 '20 at 12:03

answered Mar 05 '20 at 11:02

Arys

477
3
12

somthing like if (row.Cells["txtAttendance_Status"].Value?.ToString() == "Attended") – Ive Mar 05 '20 at 11:08
It could be done in a single line with lambda and linq but its more readable this way – Arys Mar 05 '20 at 12:04

score 0 · Answer 2 · answered Mar 05 '20 at 11:11

try
            {
                foreach (DataGridViewRow row in dataGridView2.Rows)


                        if (Convert.ToString(row.Cells["txtAttendance_Status"].Value) == "Attended")
                        {
                            row.Cells["txtStatus"].Value = true;
                        }
                        else if (Convert.ToString(row.Cells["txtAttendance_Status"].Value) == "Not Attended")
                        {
                            row.Cells["txtStatus"].Value = false;
                        }
                        else
                        {
                            row.Cells["txtStatus"].Value = false;
                        }

            }

            catch (Exception ex)
            {
                MessageBox.Show("Error", ex.ToString());
            }

score 0 · Answer 3 · answered Mar 05 '20 at 11:15

try
        {
            foreach (DataGridViewRow row in dataGridView2.Rows)


                    if (row.Cells["txtAttendance_Status"].Value.ToString() == "Attended")
                    {
                        row.Cells["txtStatus"].Value = true;
                    }
                    else if (row.Cells["txtAttendance_Status"].Value.ToString() == "Not Attended")
                    {
                        row.Cells["txtStatus"].Value = false;
                    }
                    else
                    {
                        row.Cells["txtStatus"].Value = false;
                    }

        }

        catch (Exception ex)
        {
            MessageBox.Show("Error", ex.ToString());
        }

In this code, If any database column having null value and you are trying to convert it as string, That time System.NullReferenceException is thrown.

For Example, as per your SQL table result, for "requestid" 50 the "txtAttendance_Status" having a null value and the "System.NullReferenceException" error will occur if you try to convert this null value.1

System.NullReferenceException Error Csharp

3 Answers3